The present invention generally pertains to antenna-radome systems and is particularly directed to compensation for boresight error in a bore-sighting antenna-radome system.
A radome is a protective covering for an antenna. Radomes typically are used for covering radar antennas in missiles and aircraft so as to protect the antennas from the effects of the extreme environments in which they are used. However, the radome wall includes dielectric material and as a result, the signal that is received by an antenna covered by a radome is affected by its passage through the wall of the radome to the antenna.
In a boresighting antenna-radome system for receiving signals within a given frequency band, the different frequency components of the received signal are shifted in phase by their passage through the radome wall and the phase front is tilted. This results in the received signal providing an apparent angular displacement from the true position of the target from which the signal is received. This apparent angular displacement is referred to as the boresight error.
One system for reducing the boresight error in a boresighting antenna-radome system is described in U.S. Pat. No. 3,063,654 to Youngren et al. In such system a hollow dielectric member is carried on the inner periphery of the radome and is positioned within the nose portion thereof immediate the fore end of the radome and the scanning disk of the antenna. Although such system does provide reduction of the boresight error, at one specific frequency in the received signal, by causing a phase lag at that specific frequency, it also introduces an undesired phase lag at other frequencies that are displaced from the specific frequency within the frequency band of the received signal. This effect is due to the capacitive nature of the dielectric material in the hollow member that is positioned in the nose portion of the radome.